Tachometer is not working

[CaneCutter79]

1979 Evinrude V4 85hp (model 859995R)

I have recentlyt rebuilt my motor. I just replaced the tachometer with a Quicksilver tachometer. Brand new, in box, (not used). I have tested the wiring for ignition source (12.67volts), ground (12.67), and sending unit source (about 4volts). SO the tach has a signal getting to it. This is the second tachometer I have replaced. The last one didn't work out of the box new either.

Will a weak battery or bad battery cause this issue? I'm replacing the battery. Just throwing that out there just in case.

Is there a simple test I can do to find the problem? I'd really like a working tach. It's set to 6 pulse by the way.

 

[Barnacle_Bill]

Re: Tachometer is not working

Test your rectifier.

 

[Joe Reeves]

Re: Tachometer is not working

Just in case..... The gray wire leading our of the instrument wiring harness (engine wiring to dash) is the sending (sensor) lead that connects to either the tachometer's gray lead OR the "S" terminal of the tachometer (whichever may apply).

(Small Rectifier Description & Location)
(J. Reeves)

On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.

The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:

One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.

Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue

********************
(Small Rectifier Test)
(J. Reeves)

Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.

Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

 

[CaneCutter79]

Re: Tachometer is not working

Mechanic tested rectifier during reassembly of my rebuild
We out the tech in and needle went to 0 instantly when key turned over
We assumed it was good
I found out later that it won't get a reading

I will recheck my readings at the pulse wire bit if I have 4-7 volts, its either a bad tach or something really odd. I'll check the rectifier again but he said it was good 2 days ago. Just before the tach was installed.

 

[tazrig]

Re: Tachometer is not working

Have you tried running a "good" jump wire from the rectifier straight to the tach just to rule out a funky signal wire?

 

[Joe Reeves]

Re: Tachometer is not working

Mechanic tested rectifier during reassembly of my rebuild. We out the tech in and needle went to 0 instantly when key turned over. We assumed it was good. I found out later that it won't get a reading. I will recheck my readings at the pulse wire bit if I have 4-7 volts, its either a bad tach or something really odd. I'll check the rectifier again but he said it was good 2 days ago. Just before the tach was installed.

The needle dropping to zero (0) when the key is turned on simply shows that you have the proper 12v being applied to the unit and that it is grounded properly.

Forget the 4-7 volt test!

Test the rectifier yourself as explained above..... disconnect the battery first to eliminate possible sparking, shorts, expensive errors.

Also, double check to see that the battery isn't hooked up backwards, or even hooked up properly BUT has been charged backwards!

 

[CaneCutter79]

Re: Tachometer is not working

No I have not. I will try and test the rectifier again as noted by Joe.

Thanks guys. This has been quite a frustrating event. All I want is a functioning tach..........how hard is that!

 

[CaneCutter79]

Re: Tachometer is not working

I am not totally sure if the battery was disconnected when the mechanic installed the new gauge. Is there a chance of the gauge in cas hey Hotwire touched th hey Hotwire touched the sender pole?

Also, is there a way to test the gage itself? I should be able to use the voltmeter to check for an open or closed circuit correct?

 

[V153]

Re: Tachometer is not working

Rectifiers are cheap. Buy one. Check'n clean'n double check yer connections.

Is your rectifier gettin blazin hot? Is there brownish black goo oozin outa the backside?

Doubt that both of 2 new tachs were defective outa the box. Did they not have warrantees? That said a bad rectumfrier will ruin some aftermarket tachs. Find ya a period correct OMC tach'n see what happens. I bleve 5 is the correct pole setting for a V4 btw.

 

[CaneCutter79]

Re: Tachometer is not working

Rectifier looks OK and no goo. Not hot that I'm aware of. I'll double check this weekend and check the voltages.

The gauge I was using was an era correct OMC. The new one is a Quicksilver but should work as a replacement.

I was using 6 for the previous OMC tech. Boat has sat for 2yrs and just now getting repaired (re-built powerhead). The working tech stopped working somewhere along the way. So I replaced it with another OMC tach. It didn't work either and the boat sat for 2yrs. Now I'm back to trying to get a working tach. So I'm on a 3rd tach now.

I tested the old tach by using a multimeter. I got a circuit on the ignition and ground but no circuit on the sending source and ground. Tested the new tach and got a circuit on the sending source and ground. That told me the old tach was bad and new was good. Only thing left is the rectifier.


Oh and yes.......the batteries are connected properly and not backwards. I also didn't charge the battery backwards. I may be a novice but I'm not that dumb.

 

[CaneCutter79]

Re: Tachometer is not working

So finally got a chance to check the tach today. I was following my mechanic's instructions and going to test the voltage to the sending unit wire on the tach (since that was the easiest check). I got 6 volts with the motor running and then noticed the darndest thing.........THE TACH WAS WORKING. It seems to work well now. I checked all the connections and they were all tight. Must have been a fluke or some bad connection of some time. That or when I took apart the controller where my wiring harness for the tach is connected (i was looking for bad connections or grounds, etc) then I must have fixed the problem. NOw the tach seems to be working.

Thanks for the help guys.

One last question.....
The temp gauge is getting a reading of 9.9 volts from grounding the black lead to the ground connection and the red lead to the sending unit connect that goes to the sensor on the motor. That's about right correct?

 

[CaneCutter79]

Re: Tachometer is not working

So does anyone know what the voltage resistance should be for the temp gauge on this model?

I ran the motor for about 2.5hrs on the water last weekend for my initial break-in period (and followed the recommended break-in processes). During that time, the guage never registered any temp. I also noticed that the powerhead was really cool to the touch. Way cooler than I would have expected. It wasn't cold, but it was a little warm. Guessing maybe 100-120? That's a range but I'm guessing. I'm using double oil an dthe water temp was about 45 degrees. Cold water could help keep the motor cool and hte temps down.

I just want to make sure the temp guage is working properly as well. It has power going to it. The lights on the gauge works and the purple and black wires to the wiring harness have 12.5 volts going to it. So all wires have current. The resistance reading I got at the sending unit wire was 9.9v with the engine running at idle.